Follow-up system



March 14, 1944.

L. C. WEATHERS FOLLOW-UP SYSTEM km mm Q 3 Sheets-Sheet 1 jr/mdlla fia/Jezn Filed March 28, 1941 Marh 14, 1944. Q WEA'THERS 2,343,945

FOLLOW- UP SYSTEM Filed March 28, 1941 3 Shets-Sheet 3- Patented Mar. 14, 1944 UNITED I sTATE ssrar -Nr OFFICE Leland Clay Weathers, Falls Church, Va., assignor to Vickers Incorporated, Detroit, Micln, a cor poration of Michigan Application March 28, 1941, Serial No. 385,755

Claims.

This invention relates to a follow up system and more particularly to an electrical remote control system in which a power driven member may be made to accurately follow a control member.

The new system may include one or more selfsynchronous transmitters actuated by a control member; corresponding self-synchronous receivers for controlling the movement of .the power driven member, and a prime mover controlled by the receivers for driving the power driven member. The present system makes it possible for the rotor of the receiver or receivers to be connected directly or through a gear train to. the power driven member. Voltages generated in the receivers when there is an angle of disagreement between the receivers and the corresponding transmitters are employed to control the prime mover to bring the power driven member into a position of synchronism, i. e., a position corresponding to that of the control member.

The system of the present invention in certain of its modifications eliminates the usual slip rings of the receivers. In other modifications, where such slip rings are employed, a brush pressure may be made as great as necessary to prevent contact between the brushes and the slip rings being broken when the system is subjected to mechanical shocks. This is of particular importance in controlling large caliber guns as one of the chief difiiculties encountered in fire control is the displacement of the brushes from the slip rings of the receivers by the shocks due to firing of the gun. In previous self-synchronous systems in which the torque developed in the receiver was relied upon to bring the receiver into step with the transmitter the brush pressure of necessity wasextremely'light SO'wthat the high speed receivers could accurately follow the transmitters. In the present system the rotors of the receivers are driven from a prime mover of any desired power and rugged slip ring and brush structures can be employed. Also-the receivers may be of simple construction and be provided with rugged bearings since the friction in the receiver is overcome by the torque of the prime mover instead of the torque of the receiver.

The system of the present invention is also capable of operation impulsively as the power driven member approaches a position corresponding to that of the control member so that overshooting due to the inertia of the driven member is prevented and the gun or other mechanism being controlled is brought to its desired position :apidly without hunting. Indicating receivers may also be and preferably are operated from the same transmitters and both the indicating and power control receivers may be of the three wire type in which only three'wires are required bev tween a given transmitter and its associated receiver or receivers. No friction dampers are required on the power control receivers since the rotors thereof are positively connected to the power driven member and the present invention also enables indicating receivers without dampers to be employed without danger of spinning. The impulsive operation of the control system at small angles of disagreement between the power driven member and the control member also causes slight vibration of the indicating receivers so that static friction is overcome and the indicating receivers accurately indicate the position of the transmitters and power 'control receivers. Also, the power control receivers for small angles of disagreement with the transmitters supply a voltage to the system which supplies additional torque to indicating receivers to bring them into agreement with the power control receivers thus increasing the accuracy of the indicating receivers.

An object of the present invention is, therefore, to provide an improved self-synchronous system in which voltages derived from the receivers thereof control a prime mover for bringing a power driven member to zero angle of disagreement with a control member driving the transmitters.

Another object of the invention is to provide a self-synchronous system in which no slip rings and brushes are required on the receivers.

Another object'of the invention is to provide a. self-synchronous system in which the rotors of the power control receivers are.positively connected to a power driven member the position of which is controlled by the receivers.

A further object of the invention is to provide an improved self-synchronous system in which three wires only arerequired between the transmitters and receivers.

A still further object of the invention is to provide a self-synchronous system in which control of the power driven member is impulsive for small angles of disagreement so as to prevent over shooting of said member or hunting thereof.

A still further object of the invention is to provide an improved relay for a self-synchronous system capable of operating in various ways for controlling actuation of a. prime mover by selfsynchronous receivers.

Other objects and advantages of the invention will appear in the following description of the preferred embodiments of the invention shown in the attached drawings in which:

Fig. 1 is a schematic diagram of one embodiment of the system of the present invention;

Fig, 2 is a plan view of a relay suitable for a v modified type of self-synchronous system;

Fig. 3 is a vertical ection of the relay of Fig. 2 taken on" the line 3-3 of Figs. 2 and 4;

Fig. 4 is a horizontal section taken on the line 4-4 of Fig. 3;

Fig. 5 is an enlarged vertical section of a spring contact member employed in the relays of Figs. 2 to 4 inclusive;

Fig. 6 is -a fragmentary diagrammatic view illustrating how the relays of Figs. 2 to 5 may be modified for the system of Fig. 1, and also showing the employment of shading coils;

Fig. 7 is a plan view of the core members and armature of the difierential relays showing more clearly a preferred shape of the core members and armature and also showing diagrammatically a modified connection of the windings thereon; and

Fig. 8 is a schematic diagram of a portion of a modified system showing another connection of the contacts of the differential relays.

Referring to the drawings, ll indicates a control member which may be manually or otherwise rotated and II indicates a power shaft caused to follow the rotation of the control memher It by the system of the present invention.

This system may'include a low speed transmitter I! having its-rotor I! connected to a shaft l4 provided with a gear I! meshing with a gear ll forming part of the control member II which may also include a shaft l1 and a crank disc is. The system may also include a high speed transmitter I! having its rotor connected to a shaft 2i carrying a gear 22 also meshing with the gear I on theshait ll. Shafts l4 and II may also carry indicator dials II and 24 respectively.

The stators II and 2' of the transmitters l2 and I4 respectively may be connected in parallel to secondary windings 21 and 2! upon a dual excitation transformer 28 provided with a primary winding ill connected to a suitable source 8| of single phase alternating current power. The stator windings 25 and 26 of the transmitters are preferably closed distributed winding having one secondary winding 21 of the transformer 28 connected across diametrically opposed points in the winding and the other transformer secondary winding 20 also connected across diametrically opposed points of the winding, the connection of the transformer winding 20 to the stator windings l5 and 26 being in quadratured relation to the connection of the transformer winding 21. The transformer windings 21 and 2! have no electrical connection externally of the transmitters l2 and I9 and each secondary transformer winding is preferably placed on an outer leg of a three leg transformer core. The primary winding 3. is preferably placed on the center leg of the core. This construction enables the flux produced by currents in the primary winding to induce voltages in the secondary windings 21 and I! while at the same time minimizing magnetic interaction between the secondary windings. As disclosed in my Patent No. 2,227,471 granted January '7', 1941, the ,dual excitation of transmitters, stabilizes the system and prevents hunting and spinning of any receiver of the indicating receivers thus rendering unnecessary the employment of friction damping devices therein. The employment of the three leg transformer with separation of the two secondary windings so as to minimize magnetic interaction between the secondary windings still further stabilizes the system over transformers in which both secondary windings are on the second leg of the transformer. While the single closed excited winding shown is pre-- ferred because of more efiicient use of the winding conductors and less resistance loss, two sepatre quadrature stator windings each connected to one secondary primary winding can be employed if desired.

The rotor windings i3 and 20 of the transmitters l2 and I! are phase wound windings preferably three phase. While I have shown the excited windings as being on the stator and the phase wound windings as being on the rotor, it is apparent that these windings may be interchanged between the stator and rotor but that the construction shown enables a lesser number of slip rings to be employed and also the greatest heat losses ordinarily occur in the excited winding making it preferable to place such windings upon the stator.

The phase wound windings of the slow speed transmitter l2 may be connected by the conductors I2, 33 and 34 to phase wound windings II upon one member of a low speed power control receiver 38 and the phase wound windings ll of the high speed transmitter I! may be connected by conductors 31, 38 and 39 to a phase wound winding 4|] upon one member of a high speed power control receiver 4|. The other member of the receiver 38 may be provided with two quadrature windings 42 and 41, the winding 42 having its terminals connected to a winding 44 upon one core 45 01 a differential relay 4' and the winding 43 having its terminals connected to a winding 41 upon another core, 4! of the differential relay 46. Similarly the other member of the high speed power control receiver 4| may be provided with quadrature windings 49 and II. The winding 48 may have its terminals connected to a winding 5| upon a core 52 of a diiferential relay 5! through contacts 54 and SI of the differential relay I. The other quadrature winding 54 may have its terminals connected through contacts 58 and 51 to a winding it upon another core I! of the differential relay 5!. The contacts 54 and 55 may be shunted by an impedance such as a resistor 60 and the contacts 54 and 81 may be shunted by'a similar impedance II.

The contacts 55 and 51 are carried by an insulating member 62 mechanically connected to the armature 63 of the differential relay ll so as to be moved upwardly or downwardly in Fig. l, by movement of the armature 63 toward the core 52 or the core 59 respectively. Contacts 54 and ii are carried by spring members and .44, which press the contacts 54 and 56 against the contacts 55 and 51 respectively so that the circuits through contacts 54 and 55 and 54 and l are closed when the armature 61 is in its central position. The spring members 84 and I tend to keep the armature in its central position. Movement of the armature 63 upwardly in Fig. 1 toward core 52 against the spring tension of member 65, breaks the contact 54 and BI as spring member 64 engages a stop 66 to prevent the con- Q I tact 54 from following the contact 55. Similarly movement of the armature 83 downwardly in Fig. 1, toward core 59 moves contact 51 away from contact" 50 as the spring member ll engages a stop 81 to prevent contact 56 from following contact 51. I

It will be seen that energization of winding of the differential relay 53' to a greater extent than winding 58 of this relay will cause armature 63 to move upwardly in Fig. 1 thus breaking the circuit between contacts 54 and 55 and inserting the impedance 68 into the circuit of winding 5|. Similarly when winding 58 of the differential relay is energized to a greater degree than winding 5|, the armature will move downwardly breaking the circuit between contacts 58 and 51 and inserting the impedance 8| in the circuit of winding 58, By correctly connecting the windings 5| and 58 and adjusting the spring action of the spring members 64 and 65 the armature can be made to have a continuous oscillatory motion. The result is that if the two windings are energized to the same degree the armature 83 will oscillate about a central position while if winding 5| is energized to a greater extent than winding 58 the armature 63 will oscillate about a position closer to the core 52, and, conversely, if the winding 58 is energized to a greater degree than winding 51 the armature 83 will oscillate about a position closer to the core 59.

If the direction oi the single phase field in receiver M at a given instant is indicated by the arrow 68, voltages will be induced in the windings 49 and 58'which are in phase and equal in amplitude. If the field indicated by the arrow 68 is rotated by rotating the rotor of the transmitter I9 the voltages induced in windings 49 and 58 of the transmitter 41 will still be in phase but one of these voltages will be greater in amplitude than the other. For example, if the field indicated by the arrow 68 is rotated clockwise the voltage in winding 58 will be increased and the voltage in winding 49 will be decreased. This will energize winding 58 of the differential relay 53 to a greater extent than winding 5|. The armature 83 will thereby be biased toward the core 59.

By connecting the differential relay windings 5| and 58 to the receiver windings 49 and 58 respectively so that the flux in the cores 52 and 59 of the differential relay have the same instantaneous direction through the armature 63 of the differential relay as shown by the curved arrows drawn through the armature, movement of the armature toward the core 52 decreases the reluctance of the path of the flux through the core 52 and increases the reluctance of the flux path through the core 59. This increases the total flux through the core 52 and decreases the leakage flux of the winding 5| while at the same time decreasing the total flux through the core 59 and increasing the leakage flux of the winding 58. A portion of this increased leakage flux of the winding 58 adds to the total flux flowing through the armature 83 from the pole faces of the core 52. Both of these efiects result in making the armature unstable in its central position and in increasing the pull on the armature toward one of the cores as the armature approaches such core so that the armature tends to move one way or the other from its central position even if the windings 5| and 58..are

central position and cause it to pass therethrough, thus setting up the oscillation referred to. The frequency of this oscillation may be varied within wide limits by varying one or more of the following factOrs: (1) the mass of the armature or the members moved thereby; (2) the restoring spring tension of the spring -members 64 and 85; (3) the value of the impedances 88 and SI; (4) the position of the stop members 66 and 61; and (5) the voltage applied to the windings 5| and 58 from the receiver windings 49 and 58. Thus a frequency suitable for a particular installation may be easily obtained.

A second insulating member 18 carrying contacts H and 12 may also be actuated by the armature '83 of the differential relay 53. Contacts 1| and 12 engage stationary contacts 13 and 14 respectively upon downward and upward movement respectively of the armature 63. Contacts 1| to 14, inclusive, in conjunction with contacts actuated by the armature 15 of the differential relay 49 may control a third differential relay 1B. Armature 15 of differential relay 48 is mechanically connected to an insulating mem-- ber 11 carrying contacts 18 and 19 which engagecontacts 88 and 8l respectively carried by spring members 82 and 83 respectively. Spring member 82 engages a stop 84 upon upward movement of the armature 15 to break the circuit through the contacts and spring member 83 engages a stop 85 to break the circuit through contacts 19 and 8| upon downward movement of the armature 15. Contacts 18., 88, and contacts 19, 8| are in a series circuit leading from one conductor 88 connected to one source of a single phase alternating current 89 to contacts 1| and 12 of the differential relay 53. Contact 13 of difierential relay 53 adapted to be engaged by contact, 1| on downward movement of the armature 63, is connected to a conductor 98 leading to a winding 9| upon one core 92 of the differential relay 18, and contact 14 adapted to be engaged by contact 12 upon upward movement of armature 83 of difierential relay 53, is connected to a conductor 93 leading to a winding 94 on the other core 95 of differential relay 15. The other terminals of the .windings 9| and 94 of the difierential relay 1B are connected to a conductor 91 leading to the other side of the source 89.

The armature 15 of differential relay 48 is also mechanically connected to a second insulating member 99 carrying contacts I88 and I8I which are both connected to the conductor 88 leading to one side of the source 89. A stationary contact I82 is positioned to be engaged by contact I88 upon downward movement of the armature 15 of differential relay and it will be-noted that contact I82 is connected to the conductor 98 so as to be in parallel with contact 13 of difierential relay 53. Similarly, a stationary con- 7 tact I83 is positioned to be engaged by contact equally energized. When the armature moves |8I upon upward movement of the armature 15 of the differential. relay 46 and contact I83 is connected to conductor 93 so as to be in parallel with contact 14 of relay 53. Any substantial movement of armature 15 of differential relay 48 away from its central position breaks the.

series circuit from one side of the source through contacts s and as, or 19 and 8|, so as to disable contacts 1| to 14 inclusive, of differential relay 53. However either contacts I88 and I82; or contacts III and I83, of differential relay 45, complete circuits through the windings 9| and 94 III. on thepower driven shaft II.

of differential relay 16 upon movement of the armature ll of differential relay 46.

The windings 44 and 41 of differential relay 4! are preferably connected so that the instantaneous values of flux through the armature I5 thereof are in opposite directions as shown by the curved arrows through the armature I6. Movement of the armature I! away from its central position, for example, upwardly in Fig. 1 will decrease the reluctance of the flux path through core 45 and at the same time increase the reluctance of the flux path through the core 46. The flux through the core 45 tends to increase and the leakage flux of winding 44 to decrease. The flux through the core 48 tends to decrease but theleakage flux of winding 4'! tends to increase. The. increase leakage flux from the winding 41 opposes the flux through the armature I6 from thepole faces of core 45 and also the inductance of the winding 44 on core 46 increases due to the lower reluctance in its flux path, thus restraining increase in current through winding 44, so that the flux through armature I5 from the pole faces of core 46 does not increase greatly due to movement of the armature I6 toward the core 45. For a similar reason the fluxthrough armature II from the pole faces of core 46 does not decrease greatly due to movement of the armature away from the core 46. Thus the force acting on the armature is not greatly increased by movement of the armature II toward one of the cores. By correctly adjusting the spring tension of the spring members 62 and 23 the armature 16 may be made to move upwardly or downwardly substantially proportional to the difl'erence in energization between the windings 44 and 4'! of the differential relay 46 so that this relay becomes substantially deadbeat instead of impulsive as was the case of the connection of the windings of differential relay I8.

If the direction of the single phase field in the low speed power control receiver 36 is indicated by the arrow I66, voltages are induced in windings 42 and 48 of the receiver 36, which are of the same phase and equal in amplitude. Rotation oi .the field indicated by the arrow III! by rotation of the rotor of the transmitter I2 will induce unbalanced voltages in the windings 42 and 48 of the receiver 36 to actuate the diflerential relay 46. For relatively large angles of'dismeement between the rotor of the receiver 26 and the transmitter. I2 either contacts 16 and II or I! and II are opened so that the differential relay 46 of the low speed receiver 36 takes control of the differential relay I6 through its contacts I64 to I63 inclusive. For small angles of disagreement between the receiver 26 and trans mitter I2 the contacts .Il'and III as well as contacts I9 and II of differential relay 46 are closed and contacts III. and III2 are open as well as contacts I and I63; thus control is shifted to the diflerential relay 53 of the high speed receiver 4I through its contacts II to I4 inclusive.

In the preferred embodiment of the present invention the rotor shaft I66 of the low speed receiver 36 carries a gear I61 meshing with a gear The differential relay 46 is also carried by a continuation of the shaft I66 of the low speed receiver 36 with the contact carrying insulating members 11 and II actuated by a member projecting axially in alignment with the shaft I06.

The imulating, members I1 and II are preferably held againstrotation. In order to provide for rotational the differential relay 46 with the rotor shaft III, a connection I09 permitting relative rotation between the insulating members II and 64 and the diflerential relay may be provided. Similarly the rotor shaft III! of the high speed receiver 4| may be provided with a gear IJI meshing with the gear I68 and the differential relay 63 associated with the receiver 4| may be carried by a continuation of the shaft III). Preferably the insulating member 62, spring members 64 and I6 and associated contacts and stops are also carried by the rotor shaft II 0., The insulating member III and its associated contacts are preferably held against rotation and a connection I I2 is provided between insulating member II and insulating member 62 to enable relative rotation therebetween. Axial movement may however be transmitted. throughjthe connections III! and III for moving the insulating members II and II respectively. The connection I6! is illustrated on a larger scale in Fig. 6 and may comprise a casing III attached to the insulating member 11 and having a screw threaded bore H4. An axially extending member I I6 may have an enlarged head II6 positioned with the bore II4, being held in place by a screw threaded plug III provided with a bore I I6 for the member I I6. Such a Joint provides for relative rotation while transmitting axial movement.

The differential relay I6 may control a prime mover II! which is shown by way of example as a reversible single phase induction motor of the condenser type. The rotor I26 of the motor III 3.5 may drive the shaft I I through any suitable speed reducing device such as a gear train, for example, a gear I2I 'meshingwith a gear I22 upon the shaft III) of the high speed receiver may drive the shaft II through the gear III and gear Ill. The stator winding of the motor Ill may include two quadrature windings I23 and I24 having a common terminal connected to the conductor 61 leading to one side of the source 86. The armture I24 of the differential relay I6 may be mechanically connected to contacts I25 and I26 and be adapted to alternately engage contacts I21 and I28, respectively, so as to cause rotation of the rotor I24 of the motor III in one direction or the other. Any suitable spring device (not shown) may be employed to return the armature I24 to its central position. Since only one oi the windings 9| and 64 of the differential relay I6 is energized at a given time there is no opposing force due to energization of the other winding so that the relay I6 develops much more power than the differential relays 46 or I! even if all of these relays areof the same size and construction. Thus a standard relay usable in all three positions illustrated may be employed merely with diflerent connections. The relay l4 may be -bu.lt of small size and still develop a large amount of power. If the motor II! can be small in size for a given installation the relay I6 can be dispensed with and the motor windings connected directly to the contacts IIII to I63 of differential relay 46 and II to I4 of differ-- ential'relay 53 in a manner which is apparent from Fig. i so as to energize the coils I23 and I24 of the motor. 9 directly. It is apparent that all of the contacts actuated' by the differential relay 46 may be carried on the shaft 466 of the low speed receiver 26 in which case it will-be further apparent that a plurality of slip rings will be required for connecting these contacts to external circuits.

.I38 of insulating material.

Also, all of the contacts of the differential relay 53 can be carried by the shaft IIO of the high speed receiver M in which case a plurality of slip rings will be. required for connection to'the various contacts. Alternately the differential relays 46 and 53 may be separate from their respective receivers with slip ring connections between the rotor windings of the receiversand the corresponding differential relays. In such case relays of the type disclosed in Figs. 2 to 4 may beemployed to perform the same function as the differential relays 46 and 53 shown in Fig. 1.

Referring to Figs. 2 to 4, inclusive, the differential relay may include a metallic frame I26- having side members I21 and end members. I28. The cores I29 may be positioned in slots I30 in the end members I28 and held in adjusted position by set screws I3I. The cores I28 are preferably of laminated construction and are provided with operating coils I32. Itwill be apparent that the opposed cores I29 provide a substantial diamond shaped opening therebetween in which an armature I33 preferably of laminated construction is positioned. The armature I33 is secured to a pivoted member I34 attached at its lower end to a cross shaft I35 journaled at I36 in downwardly projecting members I31 secured to the side frame members I21.

An upwardly projecting portion of the pivoted member I34 has secured thereto a cross member Cross member I38 carries a pair of end contacts I39 adapted to engage adjustable stationary contacts I40 upon movement of the armature I33 from central position. The cross member I38 also carries a pair of intermediate contacts I 4| adapted to engage a pair of spring pressed contacts I 42. The stationary contacts I40 and the spring pressed contacts I42 are supported in upstanding cross members I44 of insulating material secured to the side frame members I21.

The structure supporting the spring pressed contacts I42 is shown in large scale in Fig. The contact I42 may comprise an elongated member having a shoulder I43 intermediate its ends. The contact making end of the contact member I 42 extends through an aperture I45 in one end of a cylindrical adjusting member I46 having its outer surface screw threaded and received in a screw threaded bore I41 in the insulating cross member I44.v The adjusting member I46 has an enlarged bore I48 screw threaded for a portion of its length, the bottom of the bore providing an abutment for the shoulder I43 of the contact member I42. A threaded plug I48 is received in the bore I48 in the member I46 and a compression spring I50 is positioned between the plug I49 and the shoulder I43 to-resilientiy urge the contact I42 to the left in Fig. 5. A locking nut I5I is screw threaded upon the member I46 against the insulating member I44 for holding the device in adjusted position. It will be apparent that rotation of the supporting member I46 will move the contact member I42 toward or away from its cooperating contact I4I carried on the movable cross member I38 and that rotation of the plug I49 will adjust the spring pressure on the contact member I42.

When the armature I33 and insulating cross ,member I36 secured thereto are in central position both contacts I42 are normally adjusted to the engagement with their cooperating contacts MI. The springs I50 therebyqact as centering springs for the armature I33. Upon movement of the armature I33 and the insulating cross piece I away from central position against the action of one of the springs, the other contact member I42 will break contact with its associated 5 contact I4I since the shoulder I43 of the latter mentioned contact member I42 will prevent said contact member I42 from following its cooperate ing contact Hi. It will be appreciated that the spring pressed contact structure shown in Fig. 5

operates similarly to the diagrammatic spring pressed contact structures involving spring members 64, 65, 82 and 83 shown in Fig. 1. The structure of Fig. 5 is, therefore, preferably employed in a circuit such as shown in Fig. 1 instead of the diagrammatic spring pressed contact structure shown therein.

Referring to Fig. 6 it is apparent that instead of supporting the contacts upon the relay structure itself the movement of the armature I33 may be transmitted to contact carrying members. For example any suitable force transmitting mechanism such as a link I55, pivoted to the member I34 at I36 and a lever I51 at I58,may be employed to transmit axial motion to the axial movable member II5 carrying a contact member 11 previously described. Preferably the axially movable member H5 is coaxial with the shaft of the receiver as also previously described. Furthermore, it is preferably in alignment with the center of gravity of'the relay structure so that the relay may be carried by the shaft of a receiver without unbalancing the rotating members of the receiver. By connecting the axially movable member directly to the armature, the link I55 may be directly extended and the lever I51 eliminated.

Again referring to Fig. l the system therein disclosed may also include a low speed indicating receiver I60 and a high speed indicating receiver I6I. These receivers may include a phase wound winding I62 and I63, respectively, the winding I62 of the receiver I60 being connected through conductors 32, 33 and 34 to the phase wound winding I3 of the low speed transmitter I2 and the phase wound winding I63 of the high speed receiver IBI may be connected through conductors 31, 38 and 39 to the phase wound winding 20 of the transmitter I8. The indicating receivers I60 and I6I are preferably of the short circuited secondary type and have short circuited windings I64 and I65 respectively. The short circuited windings are preferably upon the rotor but it is apparent that these windings could be upon the stators with the phase wound windings I62 and I63 upon the rotors. In either case the rotor of the low speed receiver I is provided with a shaft I66 carrying an indicating dial I61 and the rotor of the high speed receiver I6I is provided with a shaftl68 provided with an an indicating dial I68. The shafts I06 and H0 of the low speed power receiver 36 and high speed power receiver M, respectively, may also be provided with indicating dials I10 and HI, respectively, if desired.

or) Since all of the receivers disclosed in Fig. 1 have no excitation directly from a source of alternat ng current. it is preferred to provide condenser banks I12 and I13 for supplying exciting current for the low speed and high speed 70 receivers. respectively. The condensers of these condenser banks may be of-the correct capacity or as many condenser banks as necessary may be employed to maintain the power factor of the system substantially at unity.

' Both the types of power control receivers 36 and II and the indicating receivers I" and iii of the system of Fig. 1 have two points of synchronism with their transmitters. For this reason it is preferred to gear the slow speed transmitter I! to its control shaft l1 sothat the transmitter rotates at half the speed of the control shaft l1. That is the gear I! on the shaft of the low speed transmitter II should be twice the diameter of the gear ll of the control shaft i1. Similarly the gear I01 on the shaft I06 of the low speed receiver ll should be twice the diameter of the gear I08 upon the control power shaft II. The indicating dials 21, I61 and I10 of low speed transmitter l2, indicating receiver "I, and low speed power control receive 36, respectively, are therefore graduated so that each half of the dial indicates 360. These dials will therefore directly indicate the angular position of the shaft Ii from a given reference point directly in degrees.

As indicated above the low speed transmitter l2 and power control receiver 38 control the operation of the prime mover H9 to bring the shaft II to a relatively small angle of disagreement with the control shaft l1. When a predetermined small angle of disagreement is reached the high speed system including the transmitter l9 and receiver ll takes control. Any suitable speed ratio l/n between the high speed system and the low speed system may be employed although it is convenient to make l/n equal to 1/88 to give a speed ratio of 1 to 36. It is apparent that the slow speed system must bring the shaft ll into a region within 1/2n 360 on either side of synchronism with the control shaft before the control can be transferred to the high speed system as otherwise the high speed receiver would tend to control the motor II! to drive the shaft I I away from synchronism. With the ratio of 1 to 36, this means that the slow speed system must bring the shaft II to within 1/72x360 or on either side of synchronism. In order that correct control by the high speed system be assured, it is preferable to adjust the system so that the low speed system brings the angle of disagreement between the shafts II and I1 to substantially less than 5', for example, 3 to 4 before relinquishing control to the high speed system.

The total angle of control of the high speed system for a speed, ratio of 1 to 36 is therefore always less than a 10 movement of the power shaft H and each high speed transmitter or receiver makes one half revolution for each 10' movement of the power shaft ll. Each half of the high speed dials 14, It! and Hi can, therefore be graduated from 0 to 10 and these dials will then act as verniers for the low speed dials 23, I81 and I10. Since the receivers develop their maximum torque at 45 angle of dis- Igreement instead of at 180 as with conventional receivers, their torque gradient at zero angle of disagreement is greater than for conventional receivers and larger dials can be em- Dloyed without decreasing the sensitivity of the systems. Since the self-synchronous machines rotate at half speed of conventional receivers. the indicating dials can be made larger without increasing the inertia load on the system.

The operation of the relays.v may be modified y placing shading coils I (Figs. 6 and '1) in the faces of the armature I33. Such shading coils may comprise a single turn conductor of low resistance placed in slots in faces of the armature. These shading coils resist either an increase or decrease of flux through the armature, thus producing a more uniform force on the armature minimizing the usual vibration of the armature at double the frequency of the energizing voltage and producing a greater resultant force. The shading coils also slow down the action of the armature thus making the low speed differential relay more nearly deadbeat" and decreasing the frequency of oscillation of the high speed diiferential relay. While the shading coils have been shown on the armature only, it is apparent that they can be applied to either the armature or core pole faces or both.

The shape of the core and armature also has an important bearing upon the operation of the relays. By providing a. substantially diamond shaped armature I33 with the pole faces of the cores I29 parallel to the faces of the armature and at an angle to each other, the range of movement of the armature can be increased without increasing the air gap and at the same time the forces on thevarmature are balanced laterally of the relay. The angle which the pole faces make with the direction of movement of the armature can vary to a considerable degree but best results are obtained when this angle is approximately 30. This construction also enables the pole faces of one of the cores I29 of the relay to be maintained separate from the pole faces of the other core except for a small area I16 adjacent the extreme ends of the pole faces. The external faces I11 of the ends of the cores may diverge from each other so that the magnetic interaction between the cores and between their associated windings can be controlled by varying the angle of divergence. The smaller the angle between the faces I11 the greater will be the amount of leakage flux which crosses the gap between these faces, thus causing interaction between the flux of the two cores.

By varying this angle the interaction between the flux of the two cores can be varied within wide limits so that the effect of change in leakage flux due to armature movement can be made to increase or decrease the force acting on the armature as the armature moves from central position, depending upon the connection of the windings. That is to say, if the windings are connected so that the leakage flux from one winding adds to the flux passing from the pole faces of the other core through the armature, the increase of force on the armature as the armaturer moves from central position can be made to rapidly increase if the angle between the faces I11 is made small. On the other hand connecting the windings so that the leakage from one winding opposes the flux passing from the pole faces ofthe other core through the armature, making the angle between the faces I11 small, tends to minimize any increase in force on the armature due to movement toward one of the cores. An angle in the neighborhood of between the faces I11 with the areas I16 positioned quite close together has been found to produce a relay which operates efficiently for either connection.

It is in order to further control the nature of the action of the diflerential relays, a portion of the turns on one core can be connected in the same circuit as the windings on the other core as shown in Fig. 7. Thus the main winding ill on one core I29 may be connected in series with an auxiliary winding I10 having a lesser number of turns on the other core. Similarly the main winding I88 on the other core may be connected in series with an auxiliary winding I8I on the first mentioned core. By connecting the windings so that the two windings on the same core oppose each other an increase in excitation of one circuit will cause the flux in the core having the main winding to increase while causing the flux in the other core to decrease thereby increasing the resultant force on the armature by a given unbalance of the excitation voltages for the two circuits. The reverse connection of the windings of the circuits so that the windings on one core aid each other will have the reverse effect. It will be apparent that the auxiliary windings I19 and IN could be employed to constitute the impedances inserted into the main windings I18 and I88 respectively in a manner similar to that by which the impedances 60 and GI are in-.

serted into the windings and 58 of the high speed differential relay 53 of Fig. 1. By variously connecting the main and auxiliary-windings a still further control of the frequency of oscilla: tion of the implusive relay can be obtained.

In describing the operation of the system of Fig. 1 it will be first assumed that the control shaft I1 and the controlled power shaft II are in tions the armature 15 of the low speed differen- I tial relay 46 is in central position and the contacts 18-80 and 19-8| thereof are closed. vAlso the contacts IIlII-|62 and |8I||l3 of this relay are open. The armature 63 of the high speed differential relay 53 is oscillating about a central position, since this armature is in unstable equilibrium and the contacts 54 and 55 and 56 and 51 of this relay are alternately inserting the impedances 60 and 6| into thecircuits of the windings 5| and 58, respectively, of this relay. This means that the contacts 1|-13 of this relay are being closed alternately with contacts 1214. When the contacts 1| and 13 are closed a circuit may be traced from the source 89 through conductor 88, contacts 18- -80 and 198| of differential relay 46 through contacts ll-13 of differential relay 53, conductor 99, winding 9| of difierential relay 16, and conductor 91 to the other side of the source 89. Thus, winding! of differential relay 16 is closed whenever contacts 'II and .13 are closed. In a similar manner whenever contacts 12 and 14 are closed a circuit may be traced one side of the source 89 through conductor 88, contacts I26 and I28, field winding I24 of the motor H9, and conductor 91 to theother side of the source.

, differential relay 16 are oscillating substantially from one side of the source 89 to the conductor to the other side of the source 89.

differential relay 16 operates impuisively in the same manner as differential relay 53..

When contacts I21 and I25 of differential relay 16 are closed a circuit may be traced from one sideof the source 89 through conductor 88, contacts I25 and I21, field winding I23 of the motor H9 and conductor 91 to the other side of the source. -When contacts I26 and I28 of differential about their central position no resultant rotation of rotor I20 of motor I I9 is produced because of the inertia of the motor and the parts driven thereby. These pulses are merely suiiicient to 1 somewhat vibrate the entire system so that static friction any place in the system does not permit any slight angle of disagreement to persist even in the indicating receiyers I66 and I6I.

If the control shaft I1 is rotated by the control member I8, an angle of disagreement will at least temporarily exist between the shaft I1 and the shaft II. Rotation of the rotor winding 20 of the high speed transmitter I9 will cause the field indicated by the arrow 68 to rotate in the high speed receiver 4|. This will unbalance the voltages induced in the quadrature windings 49 and 59 thereof. The armature 63 of the high speed differential relay 53 will continue to oscillate but will now oscillate about a position spaced from' the central or neutral position so that one of the pairs of contacts 1II3, or 1214 will be closed, 4

for a greater length of time than the other. If it be assumed that contacts 12 and 14 are closed for the greater length of time winding 94 of the differential relay 16 will be energized for a greater length of time than winding 9| of this relay so.

that contacts I25 and I21 are closed on an average for a greater length of time than contacts I26 and I28. A resultant torque will be produced in motor I I9 to drive the shaft II in the correct direction to eliminate the angle of disagreement between the shafts II and I1 to be substantially greater than the angle at which the low speed system takes ccntrol'the voltages induced in the windings 42 and 43 of the low speed power receiver 36 will be sufficiently unbalanced to move the armature 15 of the low speed relay 4.6 and open oneof the pairs of contacts 18 and 86 or 19 and BI. Since these pairsof. contacts are in series with the control contacts of relay 53 this will break the control circuit of the high speed differential relay 53 previously traced. Movement of the armature 15 will also close one of the pairs of con-tacts |08Ill2 or II-I83. If the contacts |66--III2 are closed a circuit may be traced from one side of the source 89, conductor 88, contacts II82, conductors 90. winding 9| of diilerentialrelay 1'6 and conductor 91 If the contacts |6I-'!03 are closed, a circuit may be traced from one side of the source 89 through conductor 88, contacts IOI-III3, conductor 93, winding 94 of diiierent'ial rela 16 and conductor 91 to. the other sid of the source. Thus one or the other of the windings 9| or of differential relay 16 will be energized to close one of the pairs of contacts |25|21, or I26-|28, to cause the motor II9 to drive the shaft II in the correct relay 16 are closed a circuit may be traced from 4 Thus, reverse impulses are, impressed upon the motor I I9, but since armature.- 63 of difierential relay 53 and the armature of the direction to reduce, the angle of disagreement between this shaft and shaft II. Under these conditions the energization of the motor is constant and full power is applied thereto. When the angle of disagreement is reduced to the predetermined angle at which the high speed system takes control, the armature I! of low speed difierential relay 48 will move back under control of a spring contact 82 or 88 so that both pairs of contacts ll-88 and 8 l88 are closed and both pairs of contacts Hill-Hi2, and lot-I88 are open. This restores control to the high speed differential relay 88 so that the shafts II and I! are brmllht to final synchronism in the mgmer previously described.

In Fig. 8 is shown a modified connection 01 the contacts of the diilerential relays. In this figure the same reference numerals used in Fig. 1 are employed for elements identical with those of Fig. 1 and the reference characters of Fig; 1 with primes are employed for elements having functions similar to those oi. corresponding elements of Fig. 1. Thus contact 54' 01' Fig. 8 is a spring pressed contact 01' the type shown in Fig. 5 and operates in a manner equivalent to the spring pressed contact 84 ct Fig. 1. Contact 54' cooperates with contact 88' and is carried by an insulating member 82' actuated by the armature or a high speed differential relay such as the relay I8 0! Fig. 1. Contact 86 is also carried by the insulating member 82 and cooperates with a spring pressed contact 81. Th pair of contacts It and 88 inserts the impedance 88 into the circuit of winding ll of the high speed ditierential relay 88 of Fig. 1 and the pair of contacts II and 81' insert the impedance 8| into the circuit of winding 88 oi the diiierential relay' ll of Fig. 1, when the corresponding pairs of contacts are opened. Contacts 'H' an 12' are carried by-"the same insulating member 82' rather than a separate insulating member and cooperate with contacts 18' and 14'. respectively, to close control circuits for the winding of differential relay I8 01' P18. 1 through conductors 80 and 88, respectively.

An insulating member 11 is operated by a low speed diflerential relay such as the relay ll of Fig. 1 and carries contacts 18' and I8 cooperating with spring pressed contacts 88' and 81', re spectively. The contacts 'I8'lll' are in series with contacts IV-J8 oi the high speed diii'erentiai relay so that the former contacts control the'operation oi the latter contacts. Contacts I8 and II of the low speed differential relay are in series with contacts 12' and 'Il'- so as to similarly control the operation or the latter contacts. Spring pressed contacts 88 and 8| are connected to conductor 88 leading to one side or the source 88. The insulating member 11' for the low speed diiierential relay also carries contacts III and Ill which cooperate with contacts I82 and I88, respectively. Contacts I88 and III are connected to one side of the source 88 by th conductor 88 and contacts I82 and Ill are connected to conductors 80 and 88 respectively in parallel with contacts 18' and 14', respectively, of the high speed differential relay.

The connection 01 Fig. 8 produces a result substantially the same as the connection shown in Fig. 1, but there are never more than two pairs of, contacts in series, whereas .in Fig. 1 the pair of contacts 18-88, the pair. of contacts 'lB-lLand either of the pairs of contacts ll-18 or II-I4 may be in series. The structure of Fig. 8 thereby improper operation. When the angle of disagreement between the low speed transmitter l2 and its power control receiver 33 of Fig. 1 is sufiicient to operate the low speed differential relay 48, for example, to move the insulating member 11' of Fig. 8 downwardly in Fig. 8, contacts I88 and I02 carried thereby are closed to complete a circuit from the source 88 through conductor 88, contacts I88 and I82 to conductor 88, one winding 8| of the diilerential relay or Fig. 1-and conductor 91 to the other side of the source 89. Under these conditions movement or the insulating member 82' by the high speed differential relay can have no effect upon the operation of differential relay i8 oi Fig. 1, as downward movement of this insulating member in Fig. 8 merely closes contacts IV-I8 in parallel with "contacts HIV-48! already closed. This circuit can be traced from the source 88 through conductor 88, spring pressed contact 80' engaging contact I8 and contacts IV-I8 of the high speed diilerential relay to the conductor 98. Movement of the insulating member 82 of the high speed differential relay upward in Fig. 8 thus closing contacts IT-I4 has no eilect upon the control circuit of difierential relay I8 since these contacts are in series with open contacts 18' and 8! A similar condition exists when the insulating member TI 01 the low speed differential moves upwardly in Fig. 8. In this case contacts lll'---ll8 close a circuit which can be traced from one side of the source 88 through conductor 88, contacts HIV- I83, conductor 83, winding 9| of differential relay 16 of Fig. 1, and conductor 81 to the other side of the source 89. Movement of insulating member 82' oi. the high speed diiierential relay, again can have no effect upon the control 01 the differential relay 18 as upward movement oi this member merely closes contacts IT-ll in parallel with contacts HIV-I83. Downward movement of the insulating member 82' of the high speed diflerential relay merely closes contacts IV-18 which are in series with open contacts ray-so ofthe low speed diilerential relay.

When the insulating member 11' of the low speed diilerentiai relay remains in central position. contacts IV-l8 and Ir-J4 or the high speed diflerential relay tal re control as both pairs of contacts IV-88' and I8'8|' or the low speed diflerentlal relay are closed.

The arrangement of Fig. 8 allows a somewhat smoother transition from low speed to high Speed control and vice versa since one control or the other is always operating whereas in the system of Fig. 1 there maybe a slight instant when no control is exercised at the time diilerential relay 8 is actuated one direction or the other. However, low speed differential 48 in Fig. 1 can be adjusted so that the armature always moves rapidly from its central position to an extreme position and there is no position in which the armature of any relay can remain stationary at other than central .position without a control being exercised by one of the relays.

While the preferred embodiment contemplates Placing the differential relays directly upon the rotor shafts of their associated power control receivers andoperating certain contacts by an axiallymovable member extending {mm the shaft so as to eliminate all slip rings on the power control receiver, it is apparent that slip rings may be employed between the receivers and their reduces contact resistance and the likelihood of 1s diii'erential relays so that the differential relays ployed between the contacts of the differential relays and conductors leading to the contacts so that'difierential relays of the types shown in Figs. 2 and 4 may be mounted upon the rotor shafts or the phase wound winding may be placed on the rotor and connected through slip rings. In any case contact pressure between the brushes and slip rings may be made as heavy as necessary to prevent dislodgment of the brushes by shock, since the rotors or power control receivers are actually turned by a'prime mover which may be of any size necessary. Also either winding of any of the receivers orv transmitters may be placed on either the stator or rotor and appropriate slip rings employed for external connection to the rotor.

While I have shown an electrical prime mover of the single phase condenser type induction motor, it is apparent that any type of reversible prime mover, eith'er electrical, hydraulic or otherwise, may be employed. For installations requiring small amounts of power in the prime mover, the differential relay 16 may be eliminated and the power control contacts of the differential relays 46 and 53 employed to directly energize the prime mover while with installations requiring large amounts of power, differential relay 16 may be employed to control further relays, gas filled thermionic tubes, c'ontactors, etc., for handling large amounts of power. Since the differential relay 16 orthe differential relays 4B and 53 can be constructed to axially move a member either way from a central position, they are particularly adapted for operation of balanced hydraulic valves to control hydraulic prime mover systems conventionally employed in fire control systems. If extreme accuracy is not important, the high speed. self syndh'ronoussystem can be omitted and all control accomplished by the low speed system. In this case the low speed differential relay can be made to operate impulsively if desired.

The dually excited transmitters disclosed are preferred, since indicating receivers having no mechanical damping device can thereby be employed. However, conventional singly excited transmitters can be employed as far as the power control receiver are concerned and can likewise be employed with indicating receivers having friction dampers for preventing hunting or spinning. Furthermore transmitters havin both A. C. and D. C. excitation, for example, those disclosed in my Patent No. 2,227,474 granted J anuary '7, 1941, may be employed in the present system and the indicating receivers with any type of transmitters may be of any suitable type.

One of the major advantages of the present invention is that the receivers impose very little load upon the transmitters. The rotors of the power control receivers are mechanically rotated by a separate prime mover. Also the power control receivers produce voltages in the system which tend to drive the transmitter in the same direction in which they are rotated to establish an angle of disagreement. This means that the rotors of these'receiversalso tend to move away from rather toward zero angle of disagreement but are mechanically rotated to the zero angle by the prime mover. When the field of on of the power control receivers, for example, the field indicated by the arrow in the transmitter 36 is out of alignment with the windings 42 and 43 unequal voltages are induced in the windings 42 and 43. If the higher voltage is induced, for example, in the winding 42, the winding 44 of, the difl'erential relay 46 is energized to a greater extent than winding 41. The armature 15 Of this relay tends to move toward the core 45 thus increasing the mum at said angle of 45.

inductance of winding 44 and decreasing the inductance Of winding 41. The currents flowing through the windings 42 and 43 are thus not proportional to the voltages induced therein and the change of inductance of the circuits including the windings 42 .and 43 is reflected, into the phase wound windings 35 modifying the currents which flow therein. It has been found that the currents which flow in the phase wound winding 35 and therefore in the phase wound winding l3 of the transmitter l2 are such as to produce a torque in the transmitter l2 which is in a direction aiding the movement of the rotor l3 by the control member l8 as the control member I8 is actuated to produce a greater angle of disagreement between the control member l8 and the shaft H.

Since the indicating receiver I does constitute a load on the transmitter I2 the torque developed in the system by the power control receiver 36 at least partly compensates for the load imposed on the transmitter by the indicating receiver. The net result is that a large number of power control receivers and indicating receivers can be controlled by a relatively small transmitter. The power control receivers, however, do take current when they are at zero angle of disagreement with their transmitter and the transmitters must be large enough to supply this current to all of the power control receivers connected thereto.

It has been found that the total current taken bythe power control receivers decreases as the angle of disagreement increases up to an angle of disagreement of 45. Thisis due to the fact that the rotor windin of the power receiver which has the greatest voltage induced therein is in a circuit in which the inductance is increased due to movement of the armature of the differential relay. The total current taken by a power control receiver reaches a minimum at an angle of disagreement of 45. On the other hand the current taken by the indicating receiver is zero at zero angle of disagreement and increases as the angle of disagreement increases up to an angle of disagreement of 45 reaching a maxi- Thus the change in current taken by the power control receivers tends to compensate for the change in current taken by the indicating receivers so that the cur rent delivered by the transmitter never exceeds the current taken by the power control receivers at zero angle of disagreement for any substantial length of time even if indicating receivers are employed and never exceed it if no indicating receivers are employed. The current taken by the power control receivers can be made relatively low in value so that relatively small transmitters can be employed without excessive heating of the transmitters.

While I have disclosed the preferred embodiments of my invention, it is understood that the details thereof maybe varied within the scope of the following claims.

Iclaim: I

.1. In a follow-up system, a self-synchronous transmitter having relatively rotatable members with exciting windingson one member and phasewound windings on the other member thereof,

a receiver having relatively rotatable members, phase-wound windings on one member of said receiver and connected to the phase-wound windings of said transmitter, a pair of windings on the other member of said receiver, one of said members of said receiver being mechanically connected to a controlled member, a. prime mover for driving said controlled member, a differential device for controlling said prime mover, each of said pair of windings being connected to a winding on said device so that unbalanced voltages in said pair of windings operate said device to cause said prime mover to bring the rotor of said ber, a difierential device carried by the rotor of said receiver for controlling said prime mover, each of said pair of windings being connected to a winding on said device so that unbalanced voltages in said pair of windings operate said device to cause said prime mover to bring the rotor of .said receiver to a position in which said voltages are balanced.

3. In a follow-up system, a self-synchronous transmitter having relatively rotatable members with exciting windings on one member and phase-wound windings, on the other member thereof, a receiver having relatively rotatable members, phase-wound windings on one member of said receiver and connected to the phasewound windings of said transmitter, a pair of windings on the other member of said receiver, one 'of said members of said receiver being mechanically connected to a controlled member, a

prime mover for driving said controlled member,

a differential device carried by the rotor of said receiver and operating a reciprocal member proa prime mover for drivingsaid controlled memiecting axially from said rotor for controlling I said prime mover, each of said pair of windings being connected to a winding on said device so that unbalanced voltages in said pairof windings operate said device to cause said prime mover to bring the rotor of said receiver to a position in which said voltages are balanced.

4. In a follow-up system, a low speed self-synchronous transmtter, a high speed self-synchronous transmitter, said transmitters each having relatively rotatable members with exciting windings on one member and phase-windings on the other member, the rotors of said transmitters being mechanically connected together, a low speed receiver and a high speed receiver, each having relatively rotatable members with phasewound windings on one member, the rotors of said receivers being mechanically connected togather and to a controlled member driven by a prime mover, the phase-wound windings of each of thetransmittersbeing connected to the phasewound windings. of the corresponding receiver,

a diiferential device for each 'ofasaid receivers having means for controlling said'prime mover,

'apairofwindingsontheothermemberotsaid receiver, each pair of windings being connected to opposed windings on the corresponding differerate the corresponding device to cause said prime mover to bring the rotor of said receivers to a position in which said voltages are balanced, said system having means for disabling the differential device corresponding to said high speed receiver at a predetermined angle of disagreement between said low speed receiver and said low speed transmitter. I

5. In a follow-up system, a sell-synchronous transmitter having relatively rotatable members with exciting windings on one member and phase-wound windings on the other member thereof, a receiver having relatively rotatable,

members, phase-wound windings on one member of said receiver and connected to the phasewound windings of said transmitter, a pair of windings on the other member of said receiver, one of said members of said receiver being mechanically connected to a controlled member, an electric motor for driving said controlled member, a differential relay for controlling said electric motor, each winding of said pair of windings being connected to a winding on raid relay so that unbalanced voltages in said pair 0; windings operate said relay to cause said electric motor to bring the rotor of said receiver to a position in which said voltages are balanced.

6. In a follow-up system, a self-synchronous transmitter having relatively rotatable members with exciting windings on one member and phasewound windings on the other member thereof, a receiver having relatively rotatable members, phase-wound windings on one member of said receiver and connected to the phase-wound windings of said transmitter, a pair of windings on the other member of said receiver, one of said members of said receiver being mechanically connected to a controlled member, a prime mover for driving said controlled member, a differential device for controlling said prime mover, each of said pair of windings being connected to a winding on said device so that unbalanced voltages in said pair of windings operate said device to cause said prime mover to bring the rotor of said receiver to a position in which said voltages are balanced, and means associated with said diflerential device for delivering pu ses of power to said prime mover tending to cause the same to rotate in opposite directions for alternate pulses, said alternate pulses being equal when said voltages are balanced and unequal when said voltages are unbalanced.

7. In a follow-up system, a self-synchronous transmitter having relatively rotatable members with exciting windings on one member and phase-wound windings on the other member thereof, a receiver having relatively rotatable members, phase-wound windings on one member of said receiver and connected to the phasewound windings of said transmitter, a pair of windings on the other member oi said receiver, one of said members of said receiver being mechanically connected to a controlled member, a prime mover for driving said controlled member, a differential device for controlling said prime mover, each of said pair of windings being con- .nected to a winding on said device so that unbalanced voltages in said pair 01' windings operate said device to cause said prime mover to bring the rotor of said receiver to a position in receiver, a differential device ceivers having means for controlling said prime- :sponding device to cause relatively rotatable members with exciting windings on one member and phase-wound windingson the other member, the rotors of said transmitters being mechanically connected together, a low speed receiver, and a high speed receiver each having relatively rotatable members with phase-wound windings on on member, the rotors of said receivers being mechanically connected together and to a controlled member driv-. en by a prime mover, the phase-wound windings of each of the transmitters being connected to the phase-wound'windings of the corresponding for each of said re mover, a pair of windings on the other member of each receiver, each pair of windings being connected to opposed windings on the corresponding differential device so that unbalanced voltages in the pair of windings of either or said receivers operate the corresponding device to cause said prime mover to bring the rotor of said receivers to a position in which said voltages are balanced, said system having means for disabling the differential devicecorresponding to said high speed receiver at a predetermined angle of disagreement between said low speed transmitter, said difierential device for said low speed receiver being provided with an armature for controlling said prime mover and being connected to cause said armature to move substantially proportional to the unbalance of the voltages in ,said pair of windings of said low speed receiver,

and said differential device for said high speed receiver being provided with an armature for controlling said prime mover and being connected to cause said armature to operate impulsively.

9. In a follow-up system, a low speed self-synchronous transmitter, a high speed self-synchroa predetermined angle of disagreement between said low speed receiver and said low speed transmitter, and said differential device for said high speed receiver being provided with an armature for controlling said prime mover and being connected to cause said armature to oscillate about a point determined by the unbalance of the voltages in said pair of windings of said high speed receiver. g V

10. In a follow-up system, a self-synchronous transmitter having relatively rotatable members with exciting windings on' one member and phase-wound windings on the other member thereof, a receiver having relativeLv rotatable members, phase-wound windings on one member of said receiver and connected to the phasewound windings of said transmitter, a pair of windings on the other member of said receiver, one of said members of said receiver being mechanically connected to a controlled member, a prime mover for driving said controlled member, a difierential device for controlling said prime mover, each of said pair of windings being connected to av control winding on'said device so that unbalanced voltages in said pair or windings op-- erate said device to cause said prime mover to bring the rotor of said receiver to a position in which said voltages are balanced, said differential device including a pair of opposed cores, each supporting one of said control windings, and an armature movable between said cores, said control windings being connected to said pair of windings so that movement or said armature between said ccres varies the impedance of the circuits including the windings of said pair ofwindings to cause said transmitter to tend to rotate away from zero angle of disagreement with said receiver. 1 I I 11. In a follow-up system, a self-synchronous 4o transmitter having relatively rotatable members nous transmitter, said transmitters each having relatively r otatabler members with exciting windings on one member and phase-wound windings on the other member, the rotors of said transmitters being mechanically connected together, a low speed receiver, and a high speed receiver each having relatively rotatable members with phasewound windings on one member, the rotors of said receivers being mechanically connected together and to a controlled member driven by a rime mover, the phase-wound windings of each of the transmitters being connected to the phasewound windings of the corresponding receiver, a differential device for each of said receivers having means for controlling said prime mover, a pair of windings on the other member of each receiver, each pair of windings being connected to opposed windings 0n the corresponding differential devicewith exciting windings on one member and'phasewound windings on the other member thereof, a power control receiver having relatively rotatable members, phase-wound windings on one member of said power control receiver and connected to the phase-wound windings of said transmitter, a pair of windings on the other member of said power control receiver, one of said members of said power control receiver being mechanically connected to a controlled membena prime mover for driving said controlled member, a differential device for controlling said prime mover, each of said pair of windings being connected to a control winding on said device so that unbalanced voltages in said pair of windings operate said device to cause said prime mover to bring the rotor of said power control receiver to a position which said voltages are balanced, an indicating receiver having phase-wound windings connected to the phase-wound winding of said transmitter and power control receiver, said differential device including a pairof opposedcores each supporting one or said control windings and an armature movable between said cores, said control windings being connected to said pair of windings so that movement of said armature between said cores varies the impedance of the circuits including the windings of said pair of windings to cause said differential device to supply voltages in' said system tending to drive said indieating receiver toward zero angle of disagreement r with said power control receiver.

12. In a follow-up system, a self-synchronous transmitter having relatively rotatable members with exciting windings on one member and phascwound windings on the other member thereof, a receiver having relatively rotatable members, phase-wound windings on one member of said receiver and connected to the phase-wound windings of said transmitter, a'pair oi windings on the other member of said receiver, one of said members of said receiver being mechanically connected to a controlled member, a prime mover for driving said controlled member, a difl'erential device for controlling said prime mover, each of said pair of control windings being connected to a winding on said device so that unbalanced voltages in said pair of windings operate said device to cause said prime mover to brin the rotor of said receiver to a position in which said voltages are unbalanced, said differential device including a pair of opposed cores supporting said control windings and providing a diamond shaped opening between the pole faces of said cores, a diamond shaped armature positioned within said opening so as to be differentially attracted by said cores, and means moved by said armature ior controlling said prime mover to cause the same to rotate in one direction upon movement of said armature in one direction from a central direction, and to rotate in the opposite direction upon movement of said armature in the opposite direction from a central position.

13. In a follow-up system, a self-synchronous transmitter having relatively rotatable members with exciting windings on one member and phase-wound windings on the other member thereof, a receiver having relatively rotatable members, phase-wound windings on one member or saidreceiver and connected to the phasewound windings of said transmitter, a pair of windings on the other member of said receiver, one of said members of said receiver being mechanically connected to a controlled member, a prime mover for driving said controlled member,

said control windings being connectedv to one of i said pair of windings, an armature having pole faces corresponding to the pole faces oi said cores and positioned so as to be movable between said cores, a prime mover mechanically connected to the rotor of said receiver, and means carried by said armature for controlling said prime mover to cause the same to rotate said rotor into a position at which said voltages are equal.

15. In a follow-up system, a self-synchronous transmitter, a self-synchronous receiver connected to said transmitter, and provided with a pair of windings in which unequal voltages are induced when an angle of disagreement exists between said transmitter and said receiver, a dii ferential device having a pair of opposed coresand a control winding on each of said cores, each of said control windings being connected to one of said pair of windings, said cores being shaped to provide a diamond shaped opening therebetween, a diamond shaped armature positioned in said opening so as to be movable between said cores, a prime mover mechanically connected to the rotor of said receiver, and means carried by said armature for controlling said prime mover to cause the same to rotate said rotor into a position at which said voltages are equal, and means including spring pressed contacts for returning said armature toward central position and for causing said armature to oscillate about a point determined by the unbalance of said voltages so as to deliver pulses of power to said a diflerential device [or controlling said prime mover, each 01' said pair of control windings being connected to a winding on said device so that unbalanced voltages in said pair or windings operate said device to cause said prime mover to bring the rotor of said receiver to a position in which said voltages are balanced, said diflerentialdevice including a pair of opposed cores supporting said control windings and having angularly disposed pole faces, an armature having pole faces corresponding to the pole faces of said cores positioned to be diilerentially attracted by said cores, and means moved (by said armature for controlling said prime mover to cause the same to rotate in one direction upon movement of said armature in one direction from a central direction, and to rotate in the opposite direction upon movement of said armature in the opposite direction Irom a central position, said control winding being connected so that leakage flux from one control winding adds to the flux in the core supporting the other control winding, and contacts carried by said armature and corn nected in the circuit of said control windings for causing oscillation of said armature about a point determined by the unbalance in said voltages.

14. In a follow-up system, a self-synchronous transmitter, a self-synchronous receiver connected to said transmitter, and provided with a pair of windings inlwhich unequal voltages are induced when an angle or disagreement exists .between said transmitter and said receiver, a differential device having a pair of opposed cores provided with angularly disposed pole faces, a control winding on each of said cores, each or prime mover to cause the same to tend to rotate in opposite directions for alternate pulses whereby unbalanced voltages supplied to said control windings cause alternate pulses to be unequal and said prime mover to rotate the rotor of said roceiver to a position at which said voltages are balanced.

16. In a follow-up system, a self-synchronous transmitter having a rotor and a stator, a sellsynchronous receiver having a rotor and a stator and being electrically connected to said transmitter, said receiver having two points of synchronism with said transmitter, a rotary control member for driving said transmitter and mechanically connected to the rotor of said transmitter or rotate at half the speed of said rotor, and a dial associated with the rotor 01' said receiver each half of said dial having similar graduations to indicate the angular position of said control'member. 1

17. In a follow-up system, a rotary control member, a low speed self-synchronous transmitter having a stator and a rotor mechanically connected to said control member to have hall the speed of said control member, a rotary controlled member, a low speed self-synchronous receiver having a stator and a rotor mechanically connected to said controlled member to have half the speed of said controlled member, said receiver being electrically connected to said transmitter and having two points of synchronism with said transmitter, a high speed self-synchronous transmitter, a high speed sell-synchronous receiver electrically connected to said high speed transmitter and having two points of syn- .a stator and a rotor, the rotor of said low speed receiver being mechanically connected to the rotor of the high speed receiver and the rotor of said low speed transmitter being mechanically connected to therotor of said high speed transsaid receiver, a control winding on the other member of said receiver, one of said members of said receiver being mechanically connected to a mitter to have a speed ratio of U11, and means controlled member, a prime mover for driving ,said controlled member, a difierential device actuated by unbalanced voltages forcontrolling said prime mover, said differential device being connected to said prime mover to maintain said prime mover substantially stationary when said voltages are balanced, a pair of circuits connected to said control winding in electrical quadrature and to said diflerential device to apply ballanced voltages to said device in at least one position ofsaid field relative to said control winding and unbalanced voltages in other positions of said field to operate said device to cause said prime mover to bring the rotor of said receiver to a position in which said voltages are balanced.

19. In a follow-up system, a self-synchronous transmitter having relatively rotatable members with exciting windings on one member and phase wound windings on the other member thereof, a receiver having relatively rotatable members, phase wound windings on one member of said receiver and connected to the phase wound windings of said transmitter for producing a field in said receiver, a control winding on the other member of said receiver, one of said members 01 said receiver being mechanically connected to a controlled member, a prime mover for driving said controlled member, a differential device acsaid prime mover, said differential device being conected to said prime mover to maintain said prime mover substantially stationary when said voltages are balanced a pair of circuits connected to said control winding at an electrical angle to each other and connected to said differential device to apply balanced voltages to said device in at least one position of said field relative to said control winding and unbalanced voltages in other positions of said field to operate said device to cause said prime mover to bring the rotor of said receiver to a position in which said voltages are balanced.

20. In a follow-up system a self-synchronous transmitter having relatively rotatable members with exciting windings on one member and phase wound windings on theother member thereof,

a receiver having relatively rotatable members,

phase wound windings on one member of said receiver and connected to the phase wound windings of'said transmitter to produce a field in said receiver, 'a winding on the other member of said receiver having( portions angularly disposed electrically with respect to each other whereby said field induces balanced voltages in said portions in at least one position of said field relative to said portions and an increased voltage in one ofv said portions and a decreased voltage in another portion 'at other positions of said field so that said voltages are unbalanced one of said members of said receiver being me" chanically connected to a controlled member, a prime mover for driving saidcontrolled member, a differential device actuated by unbalanced voltages for controlling said prime mover, said differential device being connected to said prime mover to maintain said prime mover substantially stationary when said voltages are balanced said portions being connected to said differential device for applying said unbalanced voltages to said device to operate the same and cause said prime mover to bring the rotor of said receiver to a position in which said voltages are balanced. tuated by unbalanced voltages for controlling LELAND CLAY WEATHERS. 

